Erratic nodulation and nitrogen fixation in field-grown pigeonpea [Cajanus cajan (L.) Millsp.]

Abstract

Following numerous reports of nodulation failures in pigeonpea [Cajanus cajan (L.) Millsp.] crops in New South Wales, a series of experiments was conducted in glasshouses and at 6 locations in the field. When inoculated seed was grown in moist vermiculite or in sand beds in the glasshouse, pigeonpea nodulated, and fixed N2, normally; but at 3 sites in the field, we could detect neither nodulation nor N2 fixation, despite adequate inoculation or a population of suitable rhizobia in the soil. At another site there was only sporadic occurrence of effective nodules. Nitrogen was fixed at 2 of the 3 field sites on acid soils, but at 1 site it appeared that nodulation was due to a naturally occurring population of soil rhizobia and not to the inoculant. When comparisons were made, pigeonpea was invariably inferior to symbiotically related legumes, cowpea and adzuki bean, in nodulation and N2 fixation. This inferiority was associated with substantially poorer rhizobial colonisation of pigeonpea rhizospheres. The experimental findings confirmed the anecdotal evidence that pigeonpea is an erratically nodulating grain legume on neutral and alkaline soils.

The contributions of nitrogen-fixing crop legumes to the productivity of agricultural systems

“…By contrast, another long-duration crop, pigeonpea, grew poorly and fixed relatively little N (Table 6). This reflected the erratic nodulation and yield observed in the alkaline soils of the region, which has been attributed to iron deficiency (Brockwell et al, 1991;Herridge and Holland, 1993).…”

Enhancing legume N2 fixation through plant and soil management

“…Thompson et al, 1991). Beyond this generalization, it is difficult to predict situations where inoculation might not be necessary.…”

Biological nitrogen fixation and prospects for ecological intensification in cereal-based cropping systems

“…A priority will be the implementation of strategies to establish sufficient populations of rhizobia in the soil (compatible and effective with the chosen legume species) to ensure adequate root nodulation (>1000 rhzobia g soil -1 ); especially when a new legume crop with specific rhizobial requirements is sown for the first time, in highly acidic and alkaine soils where rhizobial persistance is anticipated to be poor, or when the gap between sowing the same legume species exceeds 6 years ( Brockwell et al, 1995 , Peoples et al, 2009a ). Prospective agronomic practices to achieve this would include the use of high quality rhizobial inoculants at sowing, efficient inoculation practices, and the ameliorating of any soil conditions that are either hostile to rhizobia’s survival or results in erratic nodulation (e.g., soil pH or nutrient deficiencies; Brockwell et al, 1991 ; Brockwell et al, 1995 ; Peoples et al, 2009a ; Giller and Ronner, 2019 ; O’Hara et al, 1988 ; Vanlauwe et al, 2019 ). To achieve high %Ndfa concentrations of available soil mineral N would also need to be low at sowing (<55–85 kg N ha -1 ; Voisin et al, 2002 ; Salvagiotti et al, 2008 ) because of the inhibitory effect of high concentrations of inorganic N on nodule initiation and BNF ( Peoples et al, 2009a , Guinet et al, 2018 , Santachiara et al, 2019 ).…”